The Minor planet reference article from the English Wikipedia on 24-Apr-2004
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Minor planet

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Minor planets (or planetoid), are objects in the solar system that orbit the Sun like planets, but which are smaller than planets and not counted among them. The most common types are asteroids, comets, and trans-Neptunian objects.

Minor planets are divided into groups and families based on their orbital characteristics. It is customary to name a group of asteroids after the first member of that group to be discovered. Groups are relatively loose dynamical associations, whereas families are much "tighter" and result from the catastrophic breakup of a large parent asteroid sometime in the past. The only prominent families are Eos asteroids (mean orbital radius = 3.1 AU, eccentricity = 0.1, inclination = 10°) Themis asteroids (mean orbital radius = 3.1 AU, eccentricity = 0.1, inclination = 1°), and Koronis asteroids (mean orbital radius = 2.87 AU, eccentricity = 0.05, inclination = 1°).

Table of contents
1 Groups out to the orbit of Earth
2 Groups out to the orbit of Mars
3 Groups out to the orbit of Jupiter
4 Groups beyond the orbit of Jupiter
5 See also
6 External links

Groups out to the orbit of Earth

There are relatively few asteroids that orbit close to the Sun. Several of these groups are hypothetical at this point in time, with no members having yet been discovered; as such, the names they have been given are provisional.

Groups out to the orbit of Mars

Groups out to the orbit of Jupiter

A large number of asteroids have orbits between the orbits of Mars and Jupiter, roughly 2 to 4 AU, in a region known as the Main belt. These couldn't form a planet due to the gravitational influence of Jupiter. Jupiter's gravitational influence also results in Kirkwood gaps in the asteroid belt, orbits cleared by orbital resonance. As a result of these gaps the asteroids in this region are divided into a large number of groups. They are:

Between the Hildas and the Trojans (roughly 4.05 AU to 5.0 AU), there's a 'forbidden zone'. Aside from Thule and five objects in unstable-looking orbits, Jupiter's gravity has swept everything out of this region.

Groups beyond the orbit of Jupiter

Most of the minor planets beyond the orbit Jupiter are believed to be composed of ices and other volatiles. Many are similar to comets, differing only in that the perihelia of their orbits are too distant from the Sun to produce a significant tail.

See also

External links


The Solar System
Sun | Mercury | Venus | Earth | Moon | Mars | Asteroids | Jupiter | Saturn | Uranus | Neptune | Pluto
(For other objects and regions, see: List of solar system objects, Astronomical objects)